There was a time when walking into a familiar theatre meant entering a familiar space. You could anticipate the dynamics of the particular auditorium, the relationship of seats to stage and, accordingly, the mode of watching. However, as Lyn Gardner wrote here the other day, theatre-makers today are playing with space to the extent that this is no longer possible. Leaving aside the sprawling mazes of Punchdrunk and the intimate shoeboxes of Slung Low, even conventional theatres are being transformed to suit the needs of individual productions.

From the new, in-the-round Old Vic to the seating-starved broken space of the Bush, there have been some startling reconfigurations of venues in recent months. Yet, even when seats and stage remain unaltered, facing one another as usual, the way we watch theatre is being challenged. Already this year, I have seen several productions that have, quite literally, brought the roof down. Last week, on entering the Royal Court's main space – usually an open proscenium arch in miniature – for Mark Ravenhill's Over There, I was immediately struck by the expanse of black frame around a petite blue box of stage. There were no exits and no wings; just three walls, floor and ceiling. The same was true of Alexandra Wood's Unbroken at the Gate, where the stage seemed to have been hollowed out of a wall and covered with translucent gauze.

Intriguingly, for all the explicit liveness of Ravenhill and Wood's plays, watching both felt remarkably similar to cinema; in front of me were rows of heads, all pointed in the same direction at the same angle, silhouetted against a rectangle of light. Creating this tighter frame seems to give the action a filmic quality. Rather than looking down upon or across an open stage, we must look through a window on to it. In Over There, the three dimensions of the cube seem oddly flattened, and I read the Treadaway twins' spatial relationship more in terms of perspective than depth. It was as if the action was projected on to an imaginary screen.

Theatre's great advantage over film is that audience and performers share a single space, which is affected by the presence of both. However, the window on to the stage also acts as division: an invisible membrane that separates audience from action. Our presence feels somehow unacknowledged and our watching illicit, as if we are voyeuristically peeking into another private world. Space is theatre's greatest attribute. It takes place before us, not merely in front of us; witnessed, not simply seen. It need not be contained by frames as is film. Theatre can, and indeed ought to, break through and destroy any arbitrary borders that impose upon it. Borrowing the aesthetics of cinema is all well and good, but theatre must remain staunchly three-dimensional; its practitioners must play with space, rather than curtail it.